(A) The process of adding an e−to a neutral gaseous atom is not always exothermic it may be exothermic or endothermic.
(C) BeB
1s22s21s22s22p1
In Be 2 s subshell in fully filled
So, need high energy to remove e−as compared to B.
(D)

due to partially positive charge zeff ↑,EN↑
So, EN of C⇒CCl4>CH4
(E) Cs is most electropositive.